The primary objectives of this core are three fold. 1) to produce developmentally staged animals (e.g. pregnant, lactating or involuting) as needed by all investigators in this program project grant, 2) to provide mammary-specific and general surgical support, and 3) to assist in the morphological and histological evaluation of mammary tissues. The capability of the core to meet these objectives is detailed below. The animal core will also serve as a center for coordination of tissue sharing among investigators in the program project. It is the experience of Dr. Neville that personnel must be directly assigned from their laboratories to work with the Animal Handling Core and the Animal Resource Center in the production and management to timed pregnant and lactating mice. This function is required by all investigators on this program project. In addition there are some skilled techniques involved in the animal experiments for which a fully trained individual needs to be available for all investigators. Tissues generated by a given project may find use in other projects. Coordinated tissue sharing will facilitate these interactions across projects.